Hybrid power systems for aircraft

ABSTRACT

A hybrid power system for a vertical takeoff and landing (“VTOL”) aircraft including a first power source operable to provide a power output for at least a forward flight mode; and a second power source configured to provide a high specific power output for an altitude adjustment flight mode, the second power source including an auxiliary gas generator coupled to a turbine and a drive system. In other aspects, there is provided a VTOL aircraft and methods for providing power to a VTOL aircraft.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.15/722,672, filed Oct. 2, 2017. The disclosure of which is herebyincorporated by reference.

TECHNICAL FIELD

The present disclosure relates to aircraft and, more particularly, toaircraft power systems, components thereof, and features and methodsrelating thereto.

DESCRIPTION OF RELATED ART

Traditional aircraft, including vertical takeoff and landing (“VTOL”)aircraft, have typically included one or more traditional power systemsof the same type (e.g., a combustion engine). Aircraft that have onepower system of the same type often encounter instances in whichincreased power from additional power systems of the same type may bedesirable. In aircraft that include more than one engine of the sametype, one or more engines are often deactivated or reduced in use duringforward flight, which can lead to weight inefficiencies (e.g.,additional weight of one or more engines while such engines remaindeactivated or reduced in use during forward flight) and fuelinefficiencies (e.g., additional fuel use for one or more engines thatdo not provide meaningful power to the aircraft during forward flight).

Some VTOL aircraft have relatively small diameter propellers, whichresults in high disk loading, for vertical flight and then transition toefficient wing lift in forward flight. For example, a VTOL aircraft mayrequire two to five times the power in hover mode than is required inforward flight. If a conventional turbine engine is sized to providepower in hover, the engine is much larger and heavier than required inforward flights, which reduces available payload. A conventional turbineengine sized for peak power in hover mode operates at a small fractionof the maximum during forward flight, which reduces efficiency and cancause high specific fuel consumption. Accordingly, traditional powersystems are often inefficient for VTOL aircraft because, if a powersystem is sized to provide sufficient power during takeoff, landing, andhovering, it is often unnecessarily large and heavy for forward flight,during which lower amounts of power are typically required.

Some aircraft have included hybrid power systems that attempt to combinetraditional power systems, such as a thermal engine, with chemical orelectrical power system. However, chemical and electrical power systemsoften do not provide sufficient specific power for certain functions andmaneuvers, such as during takeoff, landing, and hovering. Furthermore,such hybrid systems do not provide sufficient specific power (or powerdensity) to provide a pilot with sufficient time to safely account forfailure of another power system.

Propulsion systems for rockets provide a very high power source.However, the direct use of hot gasses in conventional rocket propulsionsystems creates problems such as noise, flame and heat damage, and lackof adequate throttle control, etc. Accordingly, conventional rocketpropulsion systems have a high specific power, but are not directlyuseful for VTOL aircraft.

There is a need for a hybrid power system with sufficiently highspecific energy to provide a high specific power output for certainfunctions (e.g., takeoff, landing, hovering, and failure of other powersystems), while remaining lightweight and compact so as to reduce fueland weight inefficiencies.

SUMMARY

In a first aspect, there is provided a hybrid power system for avertical takeoff and landing aircraft including a first power sourceoperable to provide a power output for at least a forward flight mode;and a second power source configured to provide a high specific poweroutput for an altitude adjustment flight mode, the second power sourceincluding an auxiliary gas generator coupled to a turbine and a drivesystem.

In an embodiment, the auxiliary gas generator includes at least one ofthe following: a combustion gas generator, a decomposition gasgenerator, a cool gas generator.

In another embodiment, the altitude adjustment flight mode includes atleast one of the following: a hover mode, a transition mode, and anengine failure mode.

In still another embodiment, the auxiliary gas generator includes aplurality of gas generator cartridges; and a plenum chamber disposedbetween the turbine and the plurality of gas generator cartridges, theplenum chamber in fluid communication with the turbine and the pluralityof gas generator cartridges; wherein the auxiliary gas generator isconfigured such that each of the plurality of gas generator cartridgescan be activated independently to release gas into the plenum chamber tocontrol power output of the turbine.

In yet another embodiment, the auxiliary gas generator includes acombustion gas generator configured to use solid propellant as a fuel.

In an embodiment, the solid propellant includes a solid fuel, anoxidizer, and a cooling agent.

In one embodiment, the drive system includes at least one of thefollowing: an electric system, a hydraulic pump system, and a mechanicaldrive system.

In another embodiment, the auxiliary gas generator is a decompositiongas generator arranged to use at least one of the following: a liquiddecomposition material and a solid decomposition material.

In another embodiment, the liquid decomposition material includes highpurity hydrogen peroxide.

In still another embodiment, the solid decomposition material includesat least one of sodium azide and nitroguanidine.

In an embodiment, the auxiliary gas generator includes a cool gasgenerator.

In another embodiment, the cool gas generator includes an oxidizingchamber; a fuel chamber; and a combustion chamber in fluid communicationwith the oxidizing chamber and the fuel chamber to enable contents ofthe oxidizing chamber and the fuel chamber to be released into thecombustion chamber.

In one embodiment, the cool gas generator is configured to permitcontrol of an inlet temperature at the turbine by controlling the rateat which the contents of the oxidizing chamber and the fuel chamber arereleased into the combustion chamber.

In yet another embodiment, the cool gas generator includes an oxidizerplenum chamber in fluid communication with a plurality of oxidizercartridges; a fuel plenum chamber in fluid communication with aplurality of fuel cartridges; and a combustion chamber in fluidcommunication with the oxidizing plenum chamber and the fuel plenumchamber to enable contents of the oxidizing plenum chamber and the fuelplenum chamber to be released into the combustion chamber; wherein thecool gas generator is configured such that each of the cartridges in theplurality of oxidizer cartridges and the plurality of fuel cartridgescan be activated independently to release contents therein into theoxidizer plenum and fuel plenum, respectively.

In a second aspect, there is provided a vertical takeoff and landingaircraft including a fuselage; a wing extending from the fuselage; arotor assembly extending from the wing; and a hybrid power systemincluding a first power source coupled to the rotor assembly by a drivesystem; and a second power source coupled to the rotor assembly by thedrive system including an auxiliary gas generator configured to providea high specific power output; and a turbine configured to be incommunication with the auxiliary gas generator; wherein the hybrid powersystem is configured such that the second power source is activatedduring an altitude adjustment flight mode.

In an embodiment, the altitude adjustment flight mode includes at leastone of the following: a hover mode, a transition mode, and an enginefailure mode.

In one embodiment, the auxiliary gas generator includes at least one ofthe following: a combustion gas generator, a decomposition gasgenerator, and a cool gas generator.

In yet another embodiment, the second power source includes a specificpower of greater than 50 Watts/kilogram and a specific energy from 5Watt-hours/kilogram to 50 Watt-hours/kilogram.

In a third aspect, there is provided a method for providing power to avertical takeoff and landing aircraft including providing a first powersource; providing a second power source including an auxiliary gasgenerator and a turbine in communication with the auxiliary gasgenerator; providing a rotor assembly; powering the rotor assembly usingthe first power source to provide lift to the aircraft; and activatingthe second power source to power the rotor assembly when the aircraft isin an altitude adjustment flight mode.

In an embodiment, the auxiliary gas generator includes at least one ofthe following: a combustion gas generator, a decomposition gasgenerator, and a cool gas generator

Other aspects, features, and advantages will become apparent from thefollowing detailed description when taken in conjunction with theaccompanying drawings, which are a part of this disclosure and whichillustrate, by way of example, principles of the inventions disclosed.

DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the embodiments of thepresent disclosure are set forth in the appended claims. However, theembodiments themselves, as well as a preferred mode of use, and furtherobjectives and advantages thereof, will best be understood by referenceto the following detailed description when read in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a perspective view of a tiltrotor aircraft in helicopter mode,according to one example embodiment;

FIG. 2 is another perspective view of a tiltrotor aircraft in airplanemode, according to one example embodiment;

FIG. 3 is a perspective view of a VTOL aircraft, according to oneexample embodiment;

FIG. 4A is a graphical comparison of power systems, according to someexemplary embodiments;

FIG. 4B is a graphical representation of power required during hover,transition, and forward flight modes, according to an illustrativeembodiment;

FIG. 5 is a depiction of a power system, according to one exampleembodiment;

FIG. 6 is a depiction of another power system, according to one exampleembodiment;

FIG. 7 is a depiction of still another power system, according to oneexample embodiment;

FIG. 8 is a depiction of yet another power system, according to oneexample embodiment;

FIG. 9 is a depiction of another power system, according to one exampleembodiment; and

FIG. 10 is a top view of an aircraft, according to one exampleembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the hybrid power systems and methodstherefor are described below. In the interest of clarity, all featuresof an actual implementation may not be described in this specification.It will, of course, be appreciated that in the development of any suchactual embodiment, numerous implementation-specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem-related and business-related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time-consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure.

In the specification, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present application, the devices,members, assemblies, etc. described herein may be positioned in anydesired orientation. Thus, the use of terms such as “above,” “below,”“upper,” “lower,” or other like terms to describe a spatial relationshipbetween various components or to describe the spatial orientation ofaspects of such components should be understood to describe a relativerelationship between the components or a spatial orientation of aspectsof such components, respectively, as the devices, members, assemblies,etc. described herein may be oriented in any desired direction.

FIGS. 1-2 depict aircraft 10, which is a VTOL tiltrotor aircraft. FIGS.1-2 depict three mutually orthogonal directions X, Y, and Z forming athree-dimensional frame of reference XYZ. Longitudinal axis X 14corresponds to the roll axis that extends through the center of aircraft10. Transverse axis Y 18 is perpendicular to longitudinal axis 14 andcorresponds to the pitch axis (also known as a control pitch axis or“CPA”). The X-Y plane is considered to be “horizontal.” Vertical axis Z22 is the yaw axis and is oriented perpendicularly with respect to theX-Y plane. The X-Z plane and Y-Z plane are considered to be “vertical.”

Aircraft 10 includes fuselage 26 as a central main body. Fuselage 26extends parallel to longitudinal axis 14 from a fuselage front end 30 toa fuselage rear end 34. Aircraft 10 further includes tail member 38extending from fuselage rear end 34 of fuselage 26. Aircraft 10 includeswing 42 and wing 46 extending from fuselage 26 substantially parallel totransverse axis Y 18. Wing 42 is coupled to propulsion system 50, andwing 46 is coupled to propulsion system 54. Propulsion system 50includes rotor assembly 58, and propulsion system 54 includes rotorassembly 62. Rotor assembly 58 includes rotor hub 66 and plurality ofrotor blades 70 extending from rotor hub 66. Similarly, rotor assembly62 includes rotor hub 74 and plurality of rotor blades 78 extending fromrotor hub 74. Aircraft 10 can, for example, be coupled to and controlledwith a hybrid power system 88 connected to a drive system 16, such asone continuous drive system or a segmented drive system separated by agearbox, including electric propulsion systems, hydraulic drive systems,or conventional drive systems, as discussed in detail below.

Rotor assemblies 58 and 62 are controllable and positionable to, forexample, enable control of direction, thrust, and lift of aircraft 10.For example, FIG. 1 illustrates aircraft 10 in a first configuration, inwhich propulsion systems 50 and 54 are positioned to provide a liftingthrust to aircraft 10, if activated. In the embodiment shown in FIG. 1,propulsion systems 50 and 54 are positioned such that, if activated,aircraft 10 moves substantially in the Z direction (“helicopter mode”).In the embodiment shown in FIG. 1, aircraft 10 further includes landinggear 82 with which aircraft 10 can contact a landing surface.

FIG. 2 illustrates aircraft 10 in a second configuration, in whichpropulsion systems 50 and 54 are positioned to provide a forward thrustto aircraft 10, if activated. In the embodiment shown in FIG. 2,propulsion systems 50 and 54 are positioned such that, if activated,aircraft 10 moves substantially in the X direction (“airplane mode”). Inthe second configuration depicted in FIG. 2, wings 42 and 46 enable alifting thrust to be provided to aircraft 10. Wings 42 and 46 can beconfigured to increase the wing span and wing aspect ratio, whichthereby increases lift/draft ratio, aircraft efficiency, and fueleconomy. Though not depicted in FIGS. 1-2, propulsion systems 50 and 54can be controllably positioned in helicopter mode, airplane mode, or anyposition between helicopter mode and airplane mode to provide for adesired direction, thrust, and/or lift.

In one embodiment, shown schematically in FIGS. 1 and 2, the hybridpower system 88 includes a first power source 68 and a second powersource 90. The first power source 68 can provide a power output for atleast a forward flight mode to the drive system 16. In one embodiment,first power source 68 is a traditional combustion engine for an aircraftcoupled to the drive system 16. In other embodiments, first power source68 can be at least one of the following: a combustion engine, ahydraulic power system, an electronic power system, and a flywheel powersystem. The combustion engine can include an engine, shaft, and gearbox.The hydraulic power system can include a hydraulic pump and fluidreservoir. The electronic power system can include at least one of thefollowing: an electric generator, a battery, and a fuel cell. Theflywheel power system can comprise a mechanical power storage systemthat includes a rotor assembly (e.g., a main rotor for a helicopter)and/or a proprotor assembly for a tiltrotor (e.g. rotor assemblies 58,62) that maintains rotational energy therein. A flywheel power systemcan provide an autorotative flight mode where the rotor assembly and/orproprotor assembly turns by action of air moving up through the rotorrather than engine power driving the rotor. The flywheel power system istypically needed in an emergency flight condition, such as when one ormore engines are not operating. The flywheel power system can providethe aircraft an opportunity to land safely in the event of an enginefailure. Consequently, all single-engine helicopters must demonstratethis capability to obtain an aircraft type certification.

In an embodiment, the second power source 90 is configured to provide ahigh specific power output for an altitude adjustment flight mode. In apreferred embodiment, the second power source 90 can provide a highspecific power output into drive system 16 without the problemsdescribed above (e.g. without noise, heat and flame damage, anduncontrollable throttle). The altitude adjustment flight mode caninclude at least one of the following flight modes: a hover mode, atransition mode and an engine failure mode. The hover mode can include alanding mode and a take-off mode. The transition mode can be a flightmode including a portion of a hover mode and a portion of a forwardflight mode that can, in some embodiments, occur concurrently.

In an embodiment, the second power source 90 is different than the firstpower source 68. The second power source 90 can be power dense such thatit can provide a high specific power output and be at least one of thefollowing: volumetrically compact and lightweight. In some embodiments,the second power source 90 has a smaller footprint (e.g. smaller volume)than the first power source 68. In some embodiments, the second powersource 90 is lighter weight than the first power source 68. In preferredembodiments, second power source 90 provides a specific power outputhigher than the first power source 68 during altitude adjustment flightmodes. In some embodiments, the second power source 90 has a higherpower density than the first power source 68. In some embodiments, thesecond power source 90 can advantageously provide high power for shortdurations (in VTOL flight) with a lower total energy that can be lighterin weight and have a smaller footprint as compared to the first powersource 68. This can be particularly advantageous for VTOL aircraft withlarge power requirement differences between hover and forward flightmodes when the VTOL portion of the mission is a small amount of thetotal mission time.

In some embodiments, both the first power source 68 and second powersource 90 are activated in a flight mode. In other embodiments, only thesecond power source 90 is activated. In an embodiment, the first powersource 68 can be powered during a forward flight mode F, as shown inFIG. 4B. The second power source 90 can be powered during the hover modeH, as shown in FIG. 4B, and/or an engine failure mode. In an embodiment,as shown in FIG. 4B, the first and second power sources 68, 90 can bepowered in a transition mode T, as shown in FIG. 4B.

The second power source 90, components thereof, and features relatingthereto can provide sufficiently high specific energy for a desirableand/or required time intervals (e.g., 15 seconds, 30 seconds, 45seconds, 1 minute, 1.5 minutes, 2 minutes, 2.5 minutes, 3 minutes, 4minutes, 5 minutes, or more), which enables the second power source 90,components thereof, and features relating thereto to provide increasedpower for a time interval required for an altitude adjustment mode or toafford a pilot longer time intervals to recover from a failure ofanother power system, such as an engine.

The first and second power sources 68, 90 are coupled to the drivesystem 16. The drive system 16 can be at least one of the following: anelectric system, a hydraulic pump system, a mechanical drive system, andcombinations thereof. In an embodiment, the first and second powersources 68, 90 are operably coupled to the same type of drive system,e.g., both are coupled to a hydraulic pump system. In anotherembodiment, the first power source 68 is operably coupled to a differentor dissimilar type of drive system than the second power source 90. Inan exemplary embodiment shown in FIGS. 1-2, the first power source 68 isoperably coupled to a mechanical drive system and the second powersource 90 is operably coupled to a mechanical drive system.

In an embodiment, the second power source 90 includes an auxiliary gasgenerator 92 coupled to a turbine 96. When activated, the auxiliary gasgenerator 92 releases gas to rotate the turbine 96, which powers thedrive system 16. The auxiliary gas generator 92 with the turbine 96 canprovide a power output to the drive system 16 that can provide a highspecific power. In some embodiments, the second power source 90 includesone or more auxiliary gas generators 92 that can be coupled to turbine96. In an embodiment, the auxiliary gas generator 92 includes at leastone of a combustion gas generator, a decomposition gas generator, a coolgas generator, and combinations thereof. In some embodiments, theauxiliary gas generator 92 is operable to provide a high power outputfor at least one altitude adjustment flight mode. The auxiliary gasgenerator 92 with the turbine 96 can be activated by the pilot orautomatically controlled as part of the propulsion system 50.

FIG. 3 depicts aircraft 110, which is a VTOL hybrid quadcopterfixed-wing aircraft. Aircraft 110 includes fuselage 126 as a centralmain body. Fuselage 126 extends parallel to longitudinal axis 114 from afuselage front end 130 to a fuselage rear end 134. Aircraft 110 furtherincludes propeller 138 extending from rear end 134 of fuselage 126.Aircraft 110 has wing 142 and wing 146 extending from fuselage 126substantially parallel to transverse axis Y 118. Wing 142 is coupled toboom 150, and wing 146 is coupled to boom 154. Boom 150 and boom 154 areeach substantially parallel to longitudinal axis 114 and, therefore,substantially parallel to fuselage 126. Boom 150 and boom 154 arecoupled to tail member 156. Aircraft 110 further includes rotor assembly158 forward of wing 142 and rotor assembly 160 aft of wing 142, each ofwhich is coupled to boom 150. Aircraft 110 also includes rotor assembly162 forward of wing 146 and rotor assembly 164 aft of wing 146, each ofwhich is coupled to boom 154. Aircraft 110 can, for example, be coupledto and controlled with a power system connected to a drive system, suchas one continuous drive system or a segmented drive system separated bya gearbox, including electric propulsion systems, hydraulic drivesystems, or conventional drive systems, as discussed in detail below.

Rotor assemblies 158, 160, 162, and 164 and propeller 138 arecontrollable and positionable to, for example, enable control ofdirection, thrust, and lift of aircraft 110. For example, rotorassemblies 158, 160, 162, and 164 can, if activated, provide a liftingthrust to aircraft 110 during takeoff and landing to enable aircraft 110to move substantially in the Z direction (e.g. an altitude adjustmentflight mode). Furthermore, propeller 138 and rotor assemblies 158, 160,162, and 164 can, if activated, provide a forward thrust to aircraft 110to enable aircraft 110 to move substantially in the X direction.Additionally, wings 142 and 146 enable a lifting thrust to be providedto aircraft 110.

An exemplary hybrid power system 188 for the aircraft 110 isschematically shown in FIG. 3 and can include a first power source 168and a second power source 190. In one embodiment, the first power source168 is an electric engine with a battery. The first power source 168 iscoupled to the drive system 116 to power the propeller 138. The secondpower source 190 includes at least one auxiliary gas generator 192 witha turbine 196 operably connected to the drive system 116 and to anelectric drive system 117 to power rotor assemblies 158, 160, 162, 164.In an embodiment, the second power source 190 provides a high specificpower output and is lighter weight than the first power source 168.

FIGS. 4A-9 depict power systems, components thereof, and featuresrelating thereto. Any power system, component thereof, or featurerelating thereto depicted in FIGS. 4A-9 and/or described herein can beused in combination with aircraft 10 and/or aircraft 110 depicted inFIGS. 1-3 and aircraft 810 depicted in FIG. 10 to operate as describedherein. Additionally, the hybrid power systems, components thereof, andfeatures relating thereto depicted in FIGS. 4A-9 and/or described hereincan be used with any aircraft configured or configurable to include oneor more power systems, including helicopters, tilt wing aircraft,unmanned aerial vehicles (UAVs), and other vertical lift or VTOLaircraft, or can further be used with any device configured orconfigurable to include a power system, including devices withpropellers, windmills, and wind turbines. Further, any features of oneembodiment of the one or more power systems or components thereof inthis disclosure can be used with any other embodiment of the one or morepower systems or components thereof in this disclosure such that theother embodiment has the same or similar features, operates in the sameor similar way, or achieves the same or similar functions.

FIG. 4A depicts graph 200, which is a comparison of the specific power(in Watts/kilogram) versus specific energy (in Watt-hours/kilogram) ofvarious power systems that can be used in connection with an aircraft ofthis disclosure. Weight of an aircraft and its components, including theweight of an aircraft's one or more power systems, is taken into accountwhen selecting and/or creating power systems for numerous reasons. Forexample, as the weight of an aircraft increases, more power is requiredto provide lift for the various aircraft functions and maneuvers.Furthermore, certain aircraft, such as VTOL aircraft, require increasedpower (e.g., 2, 3, 4, 5, 6, 7, or more times as much power) for certainfunctions and maneuvers, such as during hover mode H, transition mode T,and engine failure mode in comparison to the power required duringforward flight mode F, as shown in FIG. 4B. Therefore, determiningand/or observing the specific power and/or power density of variouspower systems assists in selecting and/or creating power systems byrevealing a power system's power output for every kilogram that it addsto an aircraft's mass. Moreover, certain aircraft, such as VTOLaircraft, may require increased power levels for a sustained timeinterval, such as the time required to takeoff, land, hover for adesired time interval, and/or recover from engine failure. Therefore, ascertain power systems may be capable of providing a high power output,but incapable of sustaining such high power output for a desired timeinterval, determining and/or observing the specific energy of variouspower systems assists in selecting and/or creating power systems byrevealing a power system's available energy for every kilogram that itadds to an aircraft's mass. Additionally, fuel efficiency of a powersystem is taken into account because, for example, while a power systemmay be capable of providing increased power during certain functions andmaneuvers, some power systems may cause high specific fuel consumptionand inefficiencies in other flight modes.

For example, as depicted in FIG. 4A, compressed gas power systems 204can have a low specific power (e.g., from 1 to 10 Watts/kilogram) and alow specific energy (e.g., from 1 to 20 Watt-hours/kilogram). Compressedgas power systems 204 does not provide advantageous specific power orspecific energy relative to other power sources.

Super capacitors 208 can offer high specific power (e.g., from 60 to 800Watts/kilogram), but only enough energy (e.g., from 1 to 6Watt-hours/kilogram) to deliver the power for a short time interval(e.g., a few seconds at most). Batteries 212 can have a wide range ofspecific powers and specific energies, but typically range from 1 to 500Watts/kilogram, which is lower than many engines, and from 5 to 300Watt-hours/kilogram, respectively. Batteries 212 can provide specificenergy for several hours but the specific power of batteries 212 islower than most combustion engines 224, which does not provide anadvantage in using batteries 212 for short term, high power when acombustion engine 224 is used as the first power source 68. Flywheelpower systems 216, which can be, for example, employed in helicopterrotor systems to store energy, typically range from 5 to 80Watt-hours/kilogram of specific energy and from 8 to 300Watt-hours/kilogram in specific power. Fuel cells 220 can provide highspecific energy (e.g., from 40 to greater than 1,000Watt-hours/kilogram), but have low specific power (e.g., from 1 to 40Watts/kilogram).

A combustion engine 224 can have both high specific energy (e.g., from40 to greater than 1,000 Watt-hours/kilogram) and high specific power(e.g., from 80 to greater than 1,000 Watts/kilogram). However, aconventional combustion engine 224 is sized for the high specific powerrequired in the hover and transition modes H, T of the mission eventhough those flight modes are only a small fraction of the overallmission. This results in a large, heavy combustion engine 224 (orengines) that reduces fuel capacity and range of the VTOL aircraft. Inone embodiment, the first power source 68 can be a combustion engine 224having at least one of the following: a smaller size, weighs less, andor less power than a conventional combustion engine 224 for a VTOLaircraft. For example, the first power source 68 can include acombustion engine 224 that operates only during the transition andforward flight modes T, F and the second power source 90 provide a highspecific power output during the hover and transition flight modes H, T.In an illustrative example, the first power source 68 can be acombustion engine 224 that is a piston engine with power density of 200W/Kg and the second power source 90 can have a specific power of atleast 1,000 W/Kg. In another illustrative example, the first powersource 68 can be a combustion engine 224 that is a turbine engine with apower density of 1,100 W/Kg and the second power source 90 can have aspecific power of at least 3,000 W/Kg.

FIG. 4A further depicts specific power and specific energy ranges forillustrative embodiments of the auxiliary gas generator 92. Auxiliarygas generator 92 having a high specific power output can include atleast one of a combustion gas generator 228, a decomposition gasgenerator 232, and a cool gas generator 236. In an embodiment, theauxiliary gas generator 92 provides a high specific power output thatcan generate a specific power of greater than or equal to 30Watts/kilogram (e.g., 50 Watts/kilogram, 100 Watts/kilogram, 200Watts/kilogram, 400 Watts/kilogram, 600 Watts/kilogram, 800Watts/kilogram, 1,000 Watts/kilogram, or more) and a specific energyfrom about 5 Watt-hours/kilogram (e.g., 7.5 Watt-hours/kilogram, 8Watt-hours/kilogram, and 9 Watt-hours/kilogram) to about 50Watt-hours/kilogram (e.g., 10 Watt-hours/kilogram, 15Watt-hours/kilogram, 20 Watt-hours/kilogram, 25 Watt-hours/kilogram, 30Watt-hours/kilogram, 35 Watt-hours/kilogram, 40 Watt-hours/kilogram, 45Watt-hours/kilogram). In one embodiment, auxiliary gas generator 92provides a high specific power output that can generate a specific powerof greater than or equal to 50 Watts/kilogram and a specific energy fromabout 5 Watt-hours/kilogram to about 30 Watt-hours/kilogram.

In an embodiment, the auxiliary gas generator 92 has a specific powerhigher than the specific power of the first power source 68. In oneembodiment, the first power source 68 includes at least one of thefollowing: an electronic power source and a flywheel power source. Inanother embodiment, the auxiliary gas generator 92 has a specific energylower than the specific energy of the first power source 68. In anexemplary embodiment, the first power source 68 includes at least one ofthe following: a combustion engine and a hydraulic power source.

In an embodiment, the auxiliary gas generator 92 converts (or permitsthe conversion of) solid and/or liquid matter into gas. Two manners bywhich a gas generator can convert (or permit the conversion of) solidand/or liquid matter into gas is by combustion and decomposition. Energyreleased during such conversion can be harnessed to provide a poweroutput. In an embodiment, a solid or liquid base substance and/or fuelmaterial can expand hundreds and, even in some embodiments, thousands oftimes in volume, which generates thermal and pressure energy that can beharnessed by the auxiliary gas generator 92. The auxiliary gas generator92 can include at least one fuel cartridge and/or a plurality of fuelcartridges. In some embodiments, the fuel cartridges are lightweight andcompact as compared to compressed gas power systems 204, which requireslarge and heavy pressure vessels. The auxiliary gas generator 92 canprovide a high specific power output while being relatively lightweightand compact as compared to the first power source 68.

Combustion gas generator 228 provides one example of the auxiliary gasgenerator 92. Combustion gas generator 228 creates energy from theconversion of a solid or liquid to a gas through combustion. Gasgenerator 228 can have specific power from 60 Watts/kilogram to greaterthan 1,000 Watts/kilogram and specific energy from 8 Watt-hours/kilogramto 20 Watt-hours/kilogram, depending on the type of gas generator, whichenables gas generator 228 to provide high specific power over a timeinterval of up to several minutes and, in some instances, more.Combustion gas generator 228 provides one example of a high specificpower gas generator that can be used to harness energy from theconversion of a solid or liquid to a gas through combustion. Forexample, combustion gas generator 228 can include solid or liquidpropellant, such as a combination of, for example, oxidizer, fuel, and abinder. Combustion gas generator 228 can include at least one of thefollowing: a liquid combustion gas generator, a solid propellant gasgenerator, and combinations thereof.

In a preferred embodiment shown in FIG. 5, combustion gas generator 228is a solid propellant gas generator 304. Solid propellant combustion gasgenerator 304 uses a solid propellant that includes an oxidizer, a fuel,and a binder combined into a solid granular form. When activated, solidpropellant combustion gas generator 304 can produce energy throughconversion of the propellant by combustion into high temperature (e.g.,2,000 degrees Fahrenheit, 3,000 degrees Fahrenheit, 4,000 degreesFahrenheit, 5,000 degrees Fahrenheit, or more) and high pressure gas.Cooling agents can be introduced to the propellant, the stoichiometricratio of the fuel in the propellant can be adjusted, and/or thestoichiometric ratio of the oxidizer can be adjusted, each of which can,for example, reduce the high temperature that can result in combustiongas generator 304. Various compositions appropriate for propellant areknown in the art, for example, as described in Gas GeneratorPropellants; by Sutton, Vriesen, and Pacanowsky, available from the web:http://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/12_2_SAN%20FRANCISCO_03-68_0065.pdf;and U.S. Pat. No. 3,362,859.

Decomposition gas generator 232 can be a decomposition thermal gasgenerator. Decomposition gas generator 232 provides another example of ahigh specific power gas generator that can be used to harness energyfrom the conversion of a solid decomposing material (e.g., sodium azide,nitroguanidine, etc.) or a liquid decomposing material (e.g., highpurity hydrogen peroxide, and the like) to a gas through decomposition.When activated, decomposition gas generator 232 produces energy throughconversion of solid or liquid propellant by decomposition (e.g.,chemically) into high temperature (e.g., a temperature above about 100degrees Fahrenheit; about 500 degrees Fahrenheit; about 1,000 degreesFahrenheit; 1,500 degrees Fahrenheit; about 2,000 degrees Fahrenheit; orhigher temperatures) and high pressure gas. Decomposition gas generator232 enables conversion of solids and liquids to gas at a lowertemperature than combustion gas generator 228. Furthermore,decomposition gas generator 232 produces energy from a decomposingmaterial without solid particulate, flames, or smoke, which can improvethe life of the turbine blade as compared power sources operating athigher temperatures. In an embodiment, a decomposition gas generator 232includes a decomposing material that comprises hydrogen peroxide using asilver catalyst. Illustrative embodiments of decomposition gasgenerators 404, 500 are shown in FIGS. 6-7.

A cool gas generator 236 is another example of an auxiliary gasgenerator 92. The cool gas generator 236 can generate energy from theconversion of a solid to a gas through decomposition at ambienttemperatures. Propellant is chemically stored in solid form and, whenactivated, the propellant is released to produce gas (e.g., highlypurified oxygen, hydrogen, nitrogen, carbon dioxide, methane, high yieldgas, etc.) at ambient temperatures. Cool gas generator 236 producesenergy through conversion of solid propellant by decomposition into gas.In some embodiments, cool gas generator 236 can produce energy throughliquid decomposition. Cool gas generator 236 is typically lighterweight, require less ignition and spool-up response time, and lesscomplex than engines that employ air, for example, by eliminating acompressor and a fuel pump/injection system. When activated, cool gasgenerator 236 produces energy at temperatures at about −50 degreesCelsius to about 60 degrees Celsius. In an embodiment, the cool gasgenerator 236 is commercially available from CGG Safety & Systems(http://www.cggss.com). Illustrative embodiments of cool gas generator236 are shown in FIGS. 8-9.

The hybrid power systems and sources of this disclosure are depicted bygraphic shapes and symbols in FIGS. 5-9. Unless this disclosurespecifies otherwise, the components of the present hybrid power systemsand sources should be understood to include the same or similarcharacteristics and features as those components that are named ordescribed, though the graphic shapes and symbols may not depict eachsuch characteristic or feature. Furthermore, though the hybrid powersystems and sources in FIGS. 5-9 are depicted as one power source, oneor more such power sources or systems can be used with an aircraft, asdesired or as necessary, to provide the same or similar characteristicsand features. Similarly, though FIGS. 5-9 may depict a power sourcehaving only one component, one or more of such components can be usedwith the power source, as desired or as necessary, to provide the sameor similar characteristics and features.

FIG. 5 depicts one embodiment of a second power source 300. Second powersource 300 includes at least one gas auxiliary generator 304 (e.g., onegas generator, in the embodiment shown). Second power source 300 furtherincludes at least one turbine 308 (e.g., one turbine, in the embodimentshown) configured to be coupled to and in communication with auxiliarygas generator 304 (e.g., in fluid communication with auxiliary gasgenerator 304). In an embodiment, auxiliary gas generator 304 is a solidpropellant combustion gas generator that can be operated at temperaturesfrom about 2,000 degrees to about 5,000 degrees Fahrenheit. In anembodiment, the auxiliary gas generator 304 can include contents thereinthat can be a solid propellant. In some embodiments, the contents in thegas generator can be a liquid propellant.

Turbine 308 can have the same or similar features as turbines used toprovide power to aircraft. For example, turbine 308 can have a pluralityof blades that rotate when contacted by fluid (gas, in this embodiment)passing through turbine 308. Turbine 308 can further have a plurality ofguide vanes or nozzle vanes that encourage fluid flow from one turbineblade to another turbine blade. Turbine 308 can be an axial flowturbine, in which gas from gas generator 304 flows substantiallyparallel to central axis 312 of turbine 308, or a radial turbine, inwhich gas from gas generator 304 flows substantially radially aboutcentral axis 312 of turbine 308. Second power source 300 (and, morespecifically, turbine 308) is configured to be coupled to drive system316 of an aircraft (e.g., such as VTOL aircraft 10, VTOL aircraft 110,and the like). If the aircraft requires additional, auxiliary, orsecondary power, the second power source 300 can be activated to providea high power to drive system 316.

Drive system 316 can include an electric propulsion system having anelectric generator, a hydraulic drive system having a hydraulic pump, ora conventional drive system having a shaft and a gearbox. Another powersource, such as a power source with a higher specific energy (e.g., atraditional aircraft engine), can also be coupled to drive system 316and/or can be coupled to a separate drive system to provide additionalpower to an aircraft.

The second power source 300 can operate in a VTOL aircraft as follows. AVTOL aircraft can include one or more first power sources, such as atraditional aircraft engine, that has a high specific energy and canprovide power over a sustained time interval for a forward flight mode.The VTOL aircraft can include second power source 300, for example, toprovide additional power output to the VTOL aircraft for an altitudeadjustment flight mode, as necessary. Auxiliary gas generator 304 ofsecond power source 300 can be a combustion gas generator (e.g., withthe same or similar features and characteristics as combustion gasgenerator 228 described above). When the VTOL aircraft is in an altitudeadjustment flight mode, gas generator 304 converts (or enables theconversion of) a solid or liquid propellant to a gas through combustionto release high temperature and high pressure gas. High temperature andhigh pressure gas released from gas generator 304 passes into turbine308 to enable turbine 308 to create power, which can be transferred todrive system 316. Drive system 316 can be coupled to one or more rotors,propellers, wings, or other components that assist in providing lift forthe VTOL aircraft. Second power source 300 can be activated, forexample, when the VTOL aircraft requires increased power, such as duringtakeoff, landing, hover, and/or failure of the first power source.

FIG. 6 depicts another embodiment of a second power source 400 that caninclude at least one gas generator 404 (e.g., one gas generator, in theembodiment shown). Certain components of the second power source 400 areas described above in connection with the second power source 300,except as noted herein. In one embodiment, auxiliary gas generator 404of power source 400 can be a decomposition gas generator (e.g., with thesame or similar features and characteristics as decomposition gasgenerator 232 described above). When activated, auxiliary gas generator404 converts (or enables the conversion of) a solid or liquid propellantto a gas through decomposition to release high temperature and highpressure gas. High temperature and high pressure gas released from theauxiliary gas generator 404 passes into turbine 408 to enable turbine408 to create power, which can be transferred to drive system 416.

FIG. 7 depicts another embodiment of a second power source 500. Certaincomponents of the second power source 500 are as described above inconnection with the second power source 300, except as noted herein.Auxiliary gas generator 503 can be configured as at least one of thefollowing: a combustion gas generator, a decomposition gas generator, acool gas generator, and combinations thereof. Auxiliary gas generator503 can include at least one gas generator cartridge 504 (e.g., five gasgenerator cartridges 504, in the embodiment shown) and a plenum chamber510. In other embodiments, auxiliary gas generator 503 can include lessthan five gas generator cartridges 504 (e.g., four, three, or two) ormore than five gas generator cartridges 504 (e.g., six, seven, eight,nine, ten, or more) depending, for example, on a desired pressure andflow within auxiliary gas generator 503, on a predicted number ofinstances in which increased power is desired, and other considerations.

In some embodiments, gas cartridges 504 contain therein at least one ofthe following: a solid propellant, a liquid propellant, a soliddecomposing material, a liquid decomposing material, and combinationsthereof. In one embodiment, there can be different types of contents inthe gas cartridges 504. For example, and not limitation, one gascartridge 504 can include a solid propellant and/or a liquid propellanttherein and the other four cartridges 504 can include a decomposingmaterial therein. Gas cartridges 504 can have the same or similarfeatures and characteristics as combustion gas generator 228 anddecomposition gas generator 232 described above. It should beappreciated that gas cartridges 504 can take on a wide variety ofconfigurations (e.g. varied sizes for holding desired amounts ofcontents therein, different contents, etc.). For example, there can betwo, three or more solid or liquid propellant filled cartridges and oneor more cartridges having a decomposing material therein.

Auxiliary gas generator 503 includes a plenum chamber 510 that isconfigured to be disposed between gas generator cartridges 504 andturbine 508 (and is disposed between gas generator cartridges 504 andturbine 508, in the embodiment shown). The gas generator cartridges 504are each depicted coupled to and in fluid communication with plenumchamber 510 and can each be activated individually to enable thecontents therein to release into plenum chamber 510. Plenum chamber 510is depicted coupled to and in fluid communication with turbine 508 toenable gas within plenum chamber 510 to release into turbine 508.

Gas generator cartridges 504 can be releasable from plenum chamber 510to enable replacement of one or more of gas generator cartridges 504after use. Independent activation of each of gas generator cartridge 504advantageously enables improved control over pressure and flow withinplenum chamber 510 and turbine 508. In addition, unused cartridges 504can be used a later time in the mission or even on a separate missiongiving better flexibility in generating the gas when it is needed.Auxiliary gas generator 503 provides the opportunity for multipleseparate firings of cartridges 504 to provide multiple high specificpower outputs during one or multiple missions without needing to replaceany or all of the cartridges 504.

Auxiliary gas generator 503 can operate with a VTOL aircraft as follows.A VTOL aircraft can include a first power source, such as a traditionalaircraft engine, that has a high specific energy and can provide powerover a sustained time interval for a forward flight mode. The VTOLaircraft can include auxiliary gas generator 503 as a second powersource to, for example, provide increased power to the VTOL aircraft, asnecessary. When one or more of the gas generator cartridges 504 areactivated, one or more gas generator cartridges 504 convert (or enablethe conversion of) a solid or liquid propellant to a gas throughcombustion or decomposition to release high temperature and highpressure gas. High temperature and high pressure gas released from oneor more gas generator cartridges 504 passes into turbine 508 to enableturbine 508 to create power, which can be transferred to drive system516. The number of activated gas cartridges 504 can determine the lengthof time and/or the amount of the high specific power provided by theauxiliary gas generator 503 to the VTOL during an altitude adjustmentflight mode.

FIG. 8 depicts an embodiment of a second power source 600 that caninclude at least one auxiliary gas generator 603. Certain components ofthe second power source 600 are as described above in connection withthe second power source 500, except as noted herein. The auxiliary gasgenerator 603 can include a cool gas generator 604 and a combustionchamber 610.

Second power source 600 further includes at least one turbine 608 (e.g.,one turbine, in the embodiment shown) configured to be coupled to and influid communication with cool gas generator 604 (e.g., and is depictedcoupled to and in fluid communication with cool gas generator 604 viacombustion chamber 610). Combustion chamber 610 is configured to bedisposed between cool gas generator 604 and turbine 608. Gas generator604 is depicted coupled to and in fluid communication with combustionchamber 610 and can be activated to enable the contents of gas generator604 to release into combustion chamber 610.

In an embodiment, the auxiliary gas generator 603 can include a controlsystem 627 including control valves 621, 625 for controlling the releaseof the contents in the cool gas generator 604 into the combustionchamber 610 to regulate turbine 608 power output. The control system 627can be in communication with the combustion chamber 610 and can includea sensor (not shown) to measure combustion chamber 610 temperature andpressure.

In the embodiment shown, cool gas generator 604 includes oxidizingchamber 620 and fuel chamber 624, each of which is configured to becoupled to and in fluid communication with turbine 608 via combustionchamber 610 (e.g., and each is depicted coupled to and in fluidcommunication with turbine 608 via combustion chamber 610). The contentsof oxidizing chamber 620 and fuel chamber 624 can be released intocombustion chamber 610 via control valves 621, 625, respectively, thatare commanded by control system 627. The control valves 621, 625 canthrottle the flow of gas from the oxidizing and fuel chambers 620, 624into the combustion chamber 610 to adjust the fuel to oxidizer ratio andcontrol the temperature at the turbine 608 inlet to provide power to theturbine 608.

Auxiliary gas generator 603 can operate with a VTOL aircraft as follows.A VTOL aircraft can include a first power source, such as a traditionalaircraft engine, that has a high specific energy and can provide powerover a sustained time interval. The VTOL aircraft can include cool gasgenerator 603 as a second power source to, for example, provideincreased power to the VTOL aircraft, as necessary. The gas generator604 portion of auxiliary gas generator 603 can be a cool gas generator(e.g., with the same or similar features and characteristics as cool gasgenerator 236 described above). When activated, cool gas generator 604(and, more specifically, oxidizing chamber 620) converts (or enables theconversion of) a solid propellant to a gas through decomposition torelease gas at ambient temperature into combustion chamber 610.Similarly, when activated, cool gas generator 604 (and, morespecifically, fuel chamber 624) releases fuel into combustion chamber610. Mixture of the contents of oxidizing chamber 620 and fuel chamber624 in combustion chamber 610 creates a high temperature and highpressure gas that passes into turbine 608 to enable turbine 608 tocreate power, which can be transferred to drive system 616. Forembodiments requiring a high power density, the gases can beindividually generated by each of the oxidizing chamber 620 and fuelchamber 624 then combined in the combustion chamber 610 and expandedthrough the power turbine 608.

FIG. 9 depicts another embodiment of a second power source 700 that caninclude at least one auxiliary gas generator 703. Certain components ofthe second power source 700 are as described above in connection withthe second power source 600, except as noted herein. Cool gas generator704 is depicted coupled to and in fluid communication with combustionchamber 710 and can be activated to enable the contents of gas generator704 to release into combustion chamber 710.

In the embodiment shown, cool gas generator 704 includes at least oneoxidizer cartridge 720 a (e.g., five oxidizer cartridges 720 a, 720 b,in the embodiment shown) configured to be coupled to and in fluidcommunication with (e.g., and depicted coupled to and in fluidcommunication with) oxidizer plenum chamber 722. In other embodiments,cool gas generator 700 can include less than five oxidizer cartridges720 (e.g., four, three, or two) or more than five oxidizer cartridges720 (e.g., six, seven, eight, nine, ten, or more) depending, forexample, on a desired pressure and flow within cool gas generator 700,on a predicted number of instances in which increased power is desired,and other considerations. Gas generator 704 further includes at leastone fuel cartridge 724 a (e.g., five fuel cartridges 724 a, 724 b, inthe embodiment shown) configured to be coupled to and in fluidcommunication with (e.g., and depicted coupled to and in fluidcommunication with) fuel plenum chamber 726. In other embodiments, coolgas generator 700 can include less than five fuel cartridges 724 (e.g.,four, three, or two) or more than five fuel cartridges 724 (e.g., six,seven, eight, nine, ten, or more) depending, for example, on a desiredpressure and flow within cool gas generator 700, on a predicted numberof instances in which increased power is desired, and otherconsiderations.

In one embodiment, at least one oxidizer cartridge 720 a and one fuelcartridge 724 a has a size different from at least one of the otheroxidizer and fuel cartridges 720 b, 724 b. In an illustrative embodimentshown in FIG. 9, the oxidizer cartridge 720 a and fuel cartridge 724 aare larger than the other oxidizer and fuel cartridges 720 b, 724 b. Thelarger size oxidizer and fuel cartridges 720 a, 724 a can be used for analtitude adjustment flight mode that requires a higher specific powerthan the other flight modes (e.g., a hover mode and/or an engine failuremode can require more power than a transition mode and/or a forwardflight mode). The larger volume oxidizer and fuel cartridges 720 a, 724a contain a larger amount of oxidizer and fuel materials therein for thealtitude adjustment flight mode needing a high specific power output. Itshould be appreciated that the size of the oxidizer and/or fuelcartridges 720 a, 724 a may take on a wide variety of configurations.For example, the oxidizer cartridge 720 a may be larger or smaller thanthe fuel cartridge 724 a. In another example, the oxidizer and/or fuelcartridges 720 a, 724 a, 720 b, 724 b can be any combination of smalland large sized cartridges configured to achieve a high power output foran altitude adjustment flight mode.

Oxidizer plenum chamber 722 and fuel plenum chamber 726 are eachconfigured to be disposed between, coupled to, and in fluidcommunication with turbine 708 via combustion chamber 710 (e.g., andeach is depicted disposed between, coupled to, and in fluidcommunication with turbine 708 via combustion chamber 710). Oxidizercartridges 720 a, 720 b can each be activated individually to enable thecontents of each of oxidizer cartridges 720 a, 720 b to release intooxidizer plenum chamber 722. Oxidizer cartridges 720 a, 720 b can alsoeach be releasable from oxidizer plenum chamber 722 to enablereplacement of one or more of oxidizer cartridges 720 a, 720 b afteruse. Similarly, fuel cartridges 724 a, 724 b can each be activatedindividually to enable the contents of each of fuel cartridges 724 a,724 b to release into fuel plenum chamber 726. Fuel cartridges 724 a,724 b can also each be releasable from fuel plenum chamber 726 to enablereplacement of one or more of fuel cartridges 724 a, 724 b after use.Independent activation of each of oxidizer cartridges 720 a, 720 b andfuel cartridges 724 a, 724 b enables improved control over pressure andflow within oxidizer plenum chamber 722, fuel plenum chamber 726,combustion chamber 710, and turbine 708. The contents of oxidizer plenumchamber 722 and fuel plenum chamber 726 can be released into combustionchamber 710.

In an embodiment, cool gas generator 704 permits control of an inlettemperature at turbine 708 by controlling a rate at which fluid entersturbine 708 through, for example, control of combustion chamber 710,control of release of the contents of oxidizer plenum chamber 722,control of release of the contents of fuel plenum chamber 726, controlof release of the contents of oxidizer cartridges 720, control ofrelease of the contents of fuel cartridges 724, and the like.

In some embodiments, auxiliary gas generator 703 can include a controlsystem 727 with control valves 721, 725 to regulate the flow from theoxidizer and fuel plenum chambers 722, 726 into the combustion chamber710. Control system 727 in combination with the firing sequence of theoxidizer and fuel cartridges 720 a, 720 b, 724 a, 724 b can throttle thegas temperature and pressure in the combustion chamber 710 to controlthe mechanical power output of the turbine 708.

Auxiliary gas generator 703 can operate with a VTOL aircraft as follows.A VTOL aircraft can include a first power source, such as a traditionalaircraft engine, that has a high specific energy and can provide powerover a sustained time interval. The VTOL aircraft can include auxiliarygas generator 703 as a second power source to, for example, provideincreased power to the VTOL aircraft, as necessary. Gas generator 704 ofauxiliary gas generator 703 can be a cool gas generator (e.g., with thesame or similar features and characteristics as cool gas generator 236described above). When one or more of oxidizer cartridges 720 areactivated, cool gas generator 704 (and, more specifically, oxidizercartridges 720 and oxidizer plenum chamber 722) converts (or enables theconversion of) a solid propellant to a gas through decomposition torelease gas at ambient temperature into combustion chamber 710.Similarly, when one or more of fuel cartridges 724 are activated, gasgenerator 704 (and, more specifically, fuel cartridges 724 and fuelplenum chamber 726) releases fuel into combustion chamber 710. Themixture of the contents of oxidizer plenum chamber 722 and fuel plenumchamber 726 in combustion chamber 710 creates a high temperature andhigh pressure gas that passes into turbine 708 to enable turbine 708 tocreate power, which can be transferred to drive system 716.

For VTOL aircraft missions requiring a high power density, theembodiments of the auxiliary gas generators 603, 703 can provideadvantages over other systems. In particular, gases can be individuallygenerated by the cool gas generators 604, 704 then combined in thecombustion chamber 610, 710 and expanded through the power turbine 608,708 without exceeding thermal material limitations. In comparing theauxiliary gas generators 603, 703 to a conventional combustion engine(e.g., an “air” breathing engine), the auxiliary gas generators 603, 703do not need a compressor, fuel pump, etc. Accordingly, the auxiliary gasgenerators 603, 703 are less complex and weigh less than a conventionalcombustion engine. In addition, the ignition and spool-up response timecan be significantly shorter than a conventional combustion engine. Theauxiliary gas generators 603, 703 can provide a higher specific power ascompared to a conventional combustion engine.

As discussed above, the hybrid power systems of this disclosure,components thereof, and features relating thereto can be used incombination with an aircraft, such as a VTOL aircraft, includingaircraft 10 and/or aircraft 110 depicted in FIGS. 1-3 to operate asdescribed herein.

FIG. 10 depicts another embodiment of the hybrid power system of thisdisclosure on VTOL aircraft 810, which is a VTOL hybrid quadcopterfixed-wing aircraft. Certain features of the aircraft 810 are asdescribed above and bear similar reference characters to the aircraft110, but with a leading ‘8’ rather than a leading ‘1’. The VTOL aircraft810 is configured to provide VTOL capabilities with minimal impact onpayload and endurance and includes a quadcopter 858, 860, 862, 864configuration on twin structural booms 850, 854, which requires nearlythree times the power generated from the fixed wing 842, 846 duringflight mode. Second power source 890 includes an auxiliary gas generator892 having a compact footprint and high power output that provides twicethe normal engine power, with only a quarter of the weight of a normalengine to add torque/power to the hydraulic pump 872 during takeoff andlanding hover modes for approximately 30-60 seconds. Advantageouslyaircraft 810 has VTOL capability for takeoff and landing modes withoutsignificant reduction in fixed wing payload and range.

Aircraft 810 includes a hybrid power system 888 having a first powersource 868 and a second power source 890. First power source 868, canbe, for example, a traditional aircraft engine. First power source 868is coupled to a drive system, which, in the embodiment shown, is ahydraulic drive system including hydraulic pump 872, high pressure driveline 876, and return line 880. The hydraulic drive system is coupled torotor assemblies 858, 860, 862, and 864 and propeller 838 (each of whichincludes hydraulic motor 884) to provide power to rotor assemblies 858,860, 862, and 864 and propeller 838 (and, more specifically, tohydraulic motors 884) to enable rotor assemblies 858, 860, 862, and 864and propeller 838, through rotation, to provide lift to aircraft 810.

Second power source 890 includes an auxiliary gas generator 892 (e.g.,which can be any gas generator of this disclosure, such as, for example,gas generator 304, 404, 504, 604, and 704) coupled to and in fluidcommunication with turbine 896 (e.g., which can be any turbine of thisdisclosure, such as, for example, turbine 308, 408, 508, 608, 708,respectively) and configured to operate as described above. For example,when activated, auxiliary gas generator 892 converts (or enables theconversion of) a solid or liquid propellant to a gas through combustionto release high temperature and high pressure gas. High temperature andhigh pressure gas released from auxiliary gas generator 892 passes intoturbine 896 to enable turbine 896 to create power, which can betransferred to hydraulic drive system. Hydraulic pump 872 is coupled torotor assemblies 858, 860, 862, and 864 and propeller 838 via highpressure drive line 876 and return line 880 that assist in providinglift for aircraft 810. Second power source 890 can be activated, forexample, when aircraft 810 requires increased power, such as duringtakeoff, landing, hover, and/or failure of the first power source.

In an illustrative embodiment, auxiliary gas generator 892 has a compactfootprint and high power output that provides twice the normal enginepower while being only a quarter of the weight of a normal engine. Theauxiliary gas generator 892 can add torque/power to the hydraulic pump872 for approximately 30-60 seconds during takeoff and landing hovermodes. Advantageously the aircraft 810 with the hybrid power systemdescribed herein has VTOL capability for takeoff and landing modeswithout a significant reduction in fixed wing payload and range.

Accordingly, with use of the hybrid power system described herein, aconventional fixed wing aircraft can be modified to have VTOLcharacteristics with minimal impact to payload and endurance and withoutaltering existing power systems, notwithstanding a significant increasein power requirements to enable takeoff, landing, and hovering of anaircraft. For example, the present hybrid power system 888 can increaseaircraft power by 2, 3, 4, 5, or more times by adding only 50%, 25%,15%, 10%, or less weight to the aircraft.

Similar such modifications to existing aircraft or design of newaircraft using the present hybrid power systems can achieve the same orsimilar results. For example, other VTOL aircraft, such as tiltrotoraircraft 10 and helicopters can be modified and/or designed to includethe present hybrid power systems to increase power, such as duringtakeoff, landing, hover, and/or failure of the first power source (e.g.,an engine-out condition, which can be assisted by adding a burst ofpower when engine-out conditions occur).

The present disclosure further includes methods, such as those forproviding power to a VTOL aircraft. Such methods include, for example,providing a first power source (e.g., an engine); providing a secondpower source (e.g., one or more of second power systems 300, 400, 500,600, and 700) including an auxiliary gas generator and a turbine incommunication with the auxiliary gas generator; providing a rotorassembly; powering the rotor assembly using the first power source toprovide lift to the aircraft; and activating the second power source topower the rotor assembly when the aircraft is in an altitude adjustmentflight mode. In an embodiment, the second power source (e.g., one ormore of second power systems 300, 400, 500, 600, and 700) has a higherspecific power than the first power source and a lower specific energythan the first power source. In some embodiments, the auxiliary gasgenerator includes at least one of the following: a combustion gasgenerator, a decomposition gas generator, a cool gas generator, andcombinations thereof.

The hybrid power systems, components thereof, and features relatingthereto that are detailed above provide numerous advantages to aircraft,including VTOL aircraft. For example, the hybrid power systems,components thereof, and features relating thereto configured inaccordance with the above disclosure can provide an aircraft with one ormore power systems having high specific power and power density,affording the aircraft increased power during certain functions andmaneuvers, such as during takeoff, landing, hovering, and failure ofother power systems), as well as increased control over such highspecific power and high power density power systems. Furthermore, thehybrid power systems, components thereof, and features relating theretoare lightweight and compact relative to, for example, traditional powersystems, such as an engine, which reduces fuel inefficiencies and weightinefficiencies (e.g., increasing payload of the aircraft) that can occurfrom duplicative traditional power systems during forward flight. Thehybrid power systems described herein can be less complex than othertraditional power systems and do not require a compressor and a fuelpump/injection system.

The embodiments of the hybrid power systems described herein areparticularly advantageous for VTOL aircraft with large power requirementdifferences between hover and forward flight modes where the VTOLportion of the mission is a minimal portion of the total mission time.

The embodiments of the hybrid power systems described herein are alsoparticularly advantageous for VTOL aircraft experiencing an engineinoperative condition. In single helicopter configurations a pilot onlyhas a short window of time to take decisive action to land safely. Thepower to safely flair and land is stored as kinetic energy (e.g.,fly-wheel) in the rotor system, but quickly bleeds off in a few seconds.Multi-engine helicopters can have some reserve power, depending on theflight condition, but can also benefit from a short-term power boostprovided by the second power system 90. The additional boost of powerover a short period of time provided by the second power system 90 canprovide greater flexibility in handling engine out conditions and caneliminate operating in undesirable portion of a height velocity diagram(e.g., the “Deadman's Curve”), which is the portion of the helicopterflight envelope where a safe recovery is not possible from enginefailure.

The hybrid power systems, components thereof, and features relatingthereto that are detailed above provide numerous advantages to aircraft,including VTOL aircraft. For example, the hybrid power systems,components thereof, and features relating thereto configured inaccordance with the above disclosure can provide an aircraft with one ormore power systems having high specific power and power density,affording the aircraft increased power during certain functions andmaneuvers, such as during takeoff, landing, hovering, and failure ofother power systems), as well as increased control over such highspecific power and high power density power systems. Furthermore, thepresent hybrid power systems, components thereof, and features relatingthereto are lightweight and compact relative to, for example,traditional power systems, such as an engine, which reduces fuelinefficiencies and weight inefficiencies that can occur from duplicativetraditional power systems during forward flight.

The terms “a” and “an” are defined as one or more unless this disclosureexplicitly requires otherwise.

The term “substantially” is defined as largely, but not necessarilywholly, what is specified (and includes what is specified; e.g.,substantially 90 degrees includes 90 degrees), as understood by a personof ordinary skill in the art. In any disclosed embodiment, the terms“substantially,” “approximately,” and “about” may be substituted with“within [a percentage] of” what is specified, where the percentageincludes 0.1, 1, 5, and 10 percent.

Terms such as “first” and “second” are used only to differentiatefeatures and not to limit the different features to a particular orderor to a particular quantity.

Where numerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example,whenever a numerical range with a lower limit, R_(l), and an upper,R_(u), is disclosed, any number falling within the range is specificallydisclosed. In particular, the following numbers within the range arespecifically disclosed: R=R_(l)+k(R_(u)−R_(l)), wherein k is a variableranging from 1 percent to 100 percent with a 1 percent increment, i.e.,k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97percent, 98 percent, 99 percent, or 100 percent. Any numerical rangedefined by two R numbers as defined in the above is also specificallydisclosed and includes the two R numbers.

Use of the term “optionally” with respect to any element of a claimmeans that the element is required, or alternatively, the element is notrequired, both alternatives being within the scope of the claim.

Use of broader terms such as comprises, includes, and has (and anyderivatives of such terms, such as comprising, including, and having)should be understood to provide support for narrower terms, such asconsisting of, consisting essentially of, and comprised substantiallyof. Thus, in any of the claims, the term “consisting of,” “consistingessentially of,” or “comprised substantially of” can be substituted forany of the open-ended linking verbs recited above in order to change thescope of a given claim from what it would otherwise be using theopen-ended linking verb.

The same or similar features of one or more embodiments are sometimesreferred to with the same reference numerals within a figure or amongfigures. However, one or more features having the same reference numeralshould not be construed to indicate that any feature is limited to thecharacteristics of another feature having the same reference numeral, orthat any feature cannot already have, or cannot be modified to have,features that are different from another feature having the samereference numeral.

At least one embodiment is disclosed and variations, combinations,and/or modifications of the embodiment(s) and/or features of theembodiment(s) made by a person having ordinary skill in the art arewithin the scope of the disclosure. Alternative embodiments that resultfrom combining, integrating, and/or omitting features of theembodiment(s) are also within the scope of the disclosure. The featureor features of one embodiment may be applied to other embodiments toachieve still other embodiments, even though not described, unlessexpressly prohibited by this disclosure or the nature of theembodiments. The scope of protection is not limited by the descriptionset out above but is defined by the claims that follow, the scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated as further disclosure into the specificationand the claims are embodiment(s) of the present invention.

The claims are not intended to include, and should not be interpreted toinclude, means-plus- or step-plus-function limitations, unless such alimitation is explicitly recited in a given claim using the phrase(s)“means for” or “step for,” respectively.

What is claimed is:
 1. A hybrid power system for a vertical takeoff andlanding aircraft comprising: a first power source operable to provide apower output for at least a forward flight mode; and a second powersource configured to provide a high specific power output for analtitude adjustment flight mode, the second power source comprising anauxiliary gas generator coupled to a turbine and a drive system.
 2. Thehybrid power system of claim 1, wherein the auxiliary gas generatorcomprises at least one of the following: a combustion gas generator, anda cool gas generator.
 3. The hybrid power system of claim 1, wherein thealtitude adjustment flight mode comprises at least one of the following:a hover mode, a transition mode, and an engine failure mode.
 4. Thehybrid power system of claim 1, wherein the auxiliary gas generatorcomprises: a plurality of gas generator cartridges; and a plenum chamberdisposed between the turbine and the plurality of gas generatorcartridges, the plenum chamber in fluid communication with the turbineand the plurality of gas generator cartridges; wherein the auxiliary gasgenerator is configured such that each of the plurality of gas generatorcartridges can be activated independently to release gas into the plenumchamber to control power output of the turbine.
 5. The hybrid powersystem of claim 1, wherein the auxiliary gas generator comprises acombustion gas generator configured to use solid propellant as a fuel.6. The hybrid power system of claim 4, wherein the solid propellantcomprises a solid fuel, an oxidizer, and a cooling agent.
 7. The hybridpower system of claim 1, wherein the drive system comprises at least oneof the following: an electric system, a hydraulic pump system, and amechanical drive system.
 8. The hybrid power system of claim 1, whereinthe auxiliary gas generator comprises a cool gas generator.
 9. Thehybrid power system of claim 8, wherein the cool gas generatorcomprises: an oxidizing chamber; a fuel chamber; and a combustionchamber in fluid communication with the oxidizing chamber and the fuelchamber to enable contents of the oxidizing chamber and the fuel chamberto be released into the combustion chamber.
 10. The hybrid power systemof claim 8, wherein the cool gas generator is configured to permitcontrol of an inlet temperature at the turbine by controlling the rateat which the contents of the oxidizing chamber and the fuel chamber arereleased into the combustion chamber.
 11. The hybrid power system ofclaim 8, wherein the cool gas generator comprises: an oxidizer plenumchamber in fluid communication with a plurality of oxidizer cartridges;a fuel plenum chamber in fluid communication with a plurality of fuelcartridges; and a combustion chamber in fluid communication with theoxidizing plenum chamber and the fuel plenum chamber to enable contentsof the oxidizing plenum chamber and the fuel plenum chamber to bereleased into the combustion chamber; wherein the cool gas generator isconfigured such that each of the cartridges in the plurality of oxidizercartridges and the plurality of fuel cartridges can be activatedindependently to release contents therein into the oxidizer plenum andfuel plenum, respectively.
 12. A vertical takeoff and landing aircraftcomprising: a fuselage; a wing extending from the fuselage; a rotorassembly extending from the wing; and a hybrid power system comprising:a first power source coupled to the rotor assembly by a drive system;and a second power source coupled to the rotor assembly by the drivesystem comprising: an auxiliary gas generator configured to provide ahigh specific power output; and a turbine configured to be incommunication with the auxiliary gas generator; wherein the hybrid powersystem is configured such that the second power source is activatedduring an altitude adjustment flight mode.
 13. The aircraft of claim 12,wherein the altitude adjustment flight mode comprises at least one ofthe following: a hover mode, a transition mode, and an engine failuremode.
 14. The aircraft of claim 12, wherein the auxiliary gas generatorcomprises at least one of the following: a combustion gas generator anda cool gas generator.
 15. The aircraft of claim 12, wherein the secondpower source comprises a specific power of greater than 50Watts/kilogram and a specific energy from 5 Watt-hours/kilogram to 50Watt-hours/kilogram.
 16. A method for providing power to a verticaltakeoff and landing aircraft comprising: providing a first power source;providing a second power source comprising an auxiliary gas generatorand a turbine in communication with the auxiliary gas generator;providing a rotor assembly; powering the rotor assembly using the firstpower source to provide lift to the aircraft; and activating the secondpower source to power the rotor assembly when the aircraft is in analtitude adjustment flight mode.
 17. The method according to claim 16,wherein the auxiliary gas generator comprises at least one of thefollowing: a combustion gas generator and a cool gas generator.